Process for selective cascade deasphalting

ABSTRACT

The invention describes a process for the deasphalting of a heavy feedstock by liquid/liquid extraction, said process comprising at least two stages of deasphalting in series carried out on the feedstock to be treated making it possible to separate at least one fraction of asphalt, at least one fraction of heavy deasphalted oil, referred to as heavy DAO and at least one fraction of light deasphalted oil, referred to as light DAO, at least one of said stages of deasphalting being carried out by means of a mixture of at least one polar solvent and at least one apolar solvent, said stages of deasphalting being implemented under the subcritical conditions of the mixture of solvents used.

FIELD OF THE INVENTION

The present invention relates to the field of the treatment of crude oil. More particularly, the present invention relates to a novel process for the selective deasphalting in series of a heavy feedstock, in particular of crude oil residues, by liquid/liquid extraction.

PRIOR ART

Crude oil residues are characterized by a continuum of molecular structures of increasing polarity and molecular weights that can generally be grouped together in four families:

-   -   The family of saturated hydrocarbons comprising hydrocarbons of         saturated and unsaturated character without an aromatic ring and         having the least polar nature of the four families,     -   The family of aromatic hydrocarbons essentially comprising         aromatic and/or heteroatomic and/or polyaromatic rings that are         generally sulphur-containing and/or nitrogen-containing. This         family has a more polar nature than that of the family of the         saturated hydrocarbons.     -   The family of resins essentially comprising heteroatomic         aromatic rings that are generally sulphur-containing and/or         nitrogen-containing and/or metal-containing with metals such as         nickel and vanadium. This family also comprises polyaromatic         and/or heteroatomic polyaromatic rings. This family has an even         more polar nature than that of the family of aromatic         hydrocarbons.     -   The family of asphaltenes comprising the most polar molecular         structures of the continuum, which are of the heteroatomic         polyaromatic type. The asphaltenes are predominantly compounds         rich in sulphur-containing, and/or nitrogen-containing and/or         oxygen-containing impurities with which metals such as nickel         and vanadium are complexed.

Resins are contained in the petroleum fractions the boiling point of which is generally greater than 300° C., whereas the asphaltenes are mainly concentrated in the fractions with high boiling points generally greater than 500° C.

Among the existing processes, the crude oil residues can be subjected to a deasphalting pre-treatment well known to a person skilled in the art. The principle of deasphalting is based on separation, by precipitation, of a petroleum residue into two phases: i) a phase referred to as “deasphalted oil”, also called “oil matrix” or “oil phase” or DAO (De-Asphalted Oil) which can be upcycled by means of various refining processes; and ii) a phase referred to as “asphalt” or sometimes “pitch” containing the refractory molecular structures described above. The asphalt, due to its mediocre quality and its variable state which can pass from a solid, then to a pasty and finally to a liquid phase depending on the temperature conditions, is a product detrimental to refining systems, that should be minimized. In fact, the performances of the processes for the upcycling and conversion of the heavy feedstocks come up against limitations which are mainly governed by the presence of these so-called refractory molecular structures contained in the asphalt.

This deasphalting, called conventional deasphalting in the remainder of the text, is generally implemented using a solvent of paraffinic type.

The U.S. Pat. No. 7,857,964 describes the impact of the nature of the paraffinic solvent used in a deasphalting process on the performance of the hydrotreatment of the residues.

The U.S. Pat. No. 4,305,812 and U.S. Pat. No. 4,455,216 describe deasphalting in the form of counter-current extraction in a column with several solvents of increasing polarity injected at different heights of the column.

The patent US 2008/149534 deals with a process for cascade deasphalting, in particular in two stages. A first paraffinic solvent with 5 or 7 carbon atoms (C5 or C7) is used in order to extract the asphalt. The deasphalted oil DAO collected is then treated with another paraffinic solvent containing less carbon (C3 or C4) in order to separate a fraction comprising the resins from the oil matrix. However this process has the drawback of producing low yields of deasphalted oil DAO linked to the use of a paraffinic solvent.

The solutions proposed in the prior art are all based on conventional deasphalting which, due to its principle, has limitations in terms of yield and flexibility with regard to the upcycling envisaged for the petroleum residues. The use of solvents or of a mixture of solvents of paraffinic type in conventional deasphalting imposes a limitation on the yield of deasphalted oil DAO, said yield increasing with the molecular weight of the solvent (up to C6/C7 solvent) then levelling off at a threshold specific to each feedstock and each solvent.

The present invention makes it possible to push back the limitations described previously. It makes it possible to improve the flexibility of separation as well as the yield of upcyclable products. The implementation of such a process comprises at least two stages of deasphalting in series and makes it possible to increase the selectivity of the separation of the feedstock. It makes it possible to obtain a more varied range of fractions of molecular structures. At least one of the stages of deasphalting according to the invention is carried out by means of a mixture of at least one polar solvent and at least one apolar solvent, the proportions of said polar solvent and said apolar solvent being adjusted according to the properties of the feedstock, according to the objective of each stage of deasphalting, according to the desired yield of asphalt and/or according to the quality of the desired DAO fractions, said stages of deasphalting being carried out under the subcritical conditions of the mixture of solvents.

An object of the process according to the invention is to allow greater flexibility in the treatment of feedstocks by accessing a range of separation selectivity previously inaccessible with conventional deasphalting. The process according to the invention allows more selective adjustment of the properties of the upcyclable fractions of the feedstock of residues during its upcycling while maximizing the final yield of all of the different separated fractions of deasphalted oils DAO of the process.

DESCRIPTION OF THE FIGURES

FIG. 1 represents a diagram of deasphalting according to the invention.

FIG. 2 represents a diagram of deasphalting incorporating two separators and recycling of the solvents individually into their respective tanks.

DETAILED DESCRIPTION OF THE INVENTION

In the remainder of the text and in the above, the expression “mixture of solvents according to the invention” is understood to mean a mixture of at least one polar solvent and at least one apolar solvent according to the invention.

The process according to the invention comprises at least two stages of deasphalting in series carried out on the feedstock to be treated, making it possible to separate at least one fraction of asphalt, at least one fraction of heavy deasphalted oil, referred to as heavy DAO and at least one fraction of light deasphalted oil, referred to as light DAO, at least one of said stages of deasphalting being carried out by means of a mixture of solvents, said stages of deasphalting being implemented under the subcritical conditions of the mixture of solvents used.

The selection of the solvents as well as the proportions of said polar solvent and said apolar solvent in the mixture of solvents are adjusted, on the one hand, according to the properties of the feedstock to be treated and according to the yield of asphalt and/or the quality of the desired deasphalted fractions of heavy DAO and light DAO, and, on the other hand, according to the specifications of the subsequent upcycling processes envisaged for each of the fractions such as hydrocracking, hydrotreatment, hydroconversion, catalytic cracking, thermal cracking etc. This results in a substantial gain in terms of separation performances, the yields and the quality of the separated fractions being improved and/or optimized depending on the objective of the system in which the process according to the invention is included.

The process according to the invention, due to specific deasphalting conditions, allows greater flexibility in the treatment of the feedstocks depending on their nature, but also depending on the envisaged upcycling system downstream of said treatment. The deasphalting conditions according to the invention make it possible to overcome the limitations of the yield of deasphalted oil DAO, as imposed in conventional deasphalting by the use of paraffinic solvents. The process according to the invention, due to specific deasphalting conditions, makes it possible to go further in maintaining the solubilization in the oil matrix of all or part of the polar structures of the heavy resins and asphaltenes which are the main constituents of the asphalt phase in the case of conventional deasphalting. The invention thus makes it possible to select which type of polar structures remain solubilized in the DAO oil matrix. The asphalt extracted during the deasphalting according to the invention corresponds to the final asphalt that is essentially composed of the most refractory polyaromatic and/or heteroatomic molecular structures in the conversion and refining processes. This results in an improved total yield of deasphalted oil.

The invention thus makes it possible to obtain at least three fractions: a fraction of asphalt, a fraction of heavy deasphalted oil referred to as heavy DAO and a fraction of light deasphalted oil referred to as light DAO with greater flexibility than in the case of conventional deasphalting in terms of optimization of yield and/or quality of each of the fractions obtained.

According to the invention, the feedstock used is selected from the feedstocks of petroleum origin of the crude oil type, or a residual fraction originating from crude oils such as an atmospheric residue or a vacuum residue originating from so-called conventional crude (API degree >20°), heavy crude (API degree comprised between 10 and 20°) or extra heavy crude (API degree <10°). Said feedstock can also be a residual fraction originating from any pre-treatment or conversion stage, such as for example, hydrocracking, hydrotreatment, thermal cracking, hydroconversion of one of these crudes or one of these atmospheric residues or one of these vacuum residues. Said feedstock can also be a residual fraction originating from the direct liquefaction of coal (atmospheric or vacuum residue) with or without hydrogen, with or without catalyst, irrespective of the process used or also a residual fraction originating from the direct liquefaction of ligno-cellulosic biomass alone or in a mixture with coal and/or a fraction of residual petroleum, with or without hydrogen, with or without catalyst, irrespective of the process used.

The boiling point of the feedstock according to the process of the invention is generally greater than 300° C., preferably greater than 400° C., more preferably greater than 450° C.

The feedstock can be of different geographic and geochemical origins (type I, II, IIS or III), and also of different degrees of maturity and biodegradation.

The feedstock according to the process of the invention can have a sulphur content greater than 0.5% m/m (percentage expressed as mass of sulphur relative to the mass of feedstock), preferably greater than 1% m/m, more preferably greater than 2% m/m, even more preferably greater than 4% m/m; a metals content greater than 20 ppm (parts per million expressed as mass of metals relative to the mass of feedstock), preferably greater than 70 ppm, preferably greater than 100 ppm, more preferably greater than 200 ppm; a C7 asphaltenes content greater than 1% m/m (percentage expressed as mass of C7 asphaltenes relative to the mass of feedstock, measured according to the NF T60-115 method), preferably greater than 3% m/m, preferably greater than 8% m/m, more preferably greater than 14% m/m; a Conradson carbon content (also called CCR) greater than 5% m/m (percentage expressed as mass of CCR relative to the mass of feedstock), preferably greater than 7% m/m, preferably greater than 14% m/m, more preferably greater than 20% m/m. Advantageously, the level of C7 asphaltenes is comprised between 1 and 40% and preferably between 2 and 30% by weight.

The stages of deasphalting of the process according to the invention can be carried out in an extraction column or extractor, preferably in a mixer-settler. Preferably, the mixture of solvents according to the invention is introduced into an extraction column or a mixer-settler, at two different levels. Preferably, the mixture of solvents according to the invention is introduced into an extraction column or a mixer-settler, at a single introduction level.

According to the invention, the liquid/liquid extraction of the stages of deasphalting is implemented under the subcritical conditions for said mixture of solvents, i.e. at a temperature less than the critical temperature of the mixture of solvents. When a single solvent, preferably an apolar solvent, is utilized, the stage of deasphalting is implemented under the subcritical conditions for said solvent, i.e. at a temperature less than the critical temperature of said solvent. The extraction temperature is advantageously comprised between 50 and 350° C., preferably between 90 and 320° C., more preferably between 100 and 310° C., even more preferably between 120 and 310° C., even more preferably between 150 and 310° C. and the pressure is advantageously comprised between 0.1 and 6 MPa, preferably between 2 and 6 MPa.

The ratio of the volume of the mixture of solvents according to the invention (volume of polar solvent+volume of apolar solvent) to the mass of feedstock is generally comprised between 1/1 and 10/1, preferably between 2/1 to 8/1 expressed as litres per kilogram.

The mixture of solvents used in at least one of the stages of selective deasphalting according to the invention is a mixture of at least one polar solvent and at least one apolar solvent.

Advantageously, the proportion of polar solvent in the mixture of polar solvent and apolar solvent is comprised between 0.1 and 99.9%, preferably between 0.1 and 95%, preferably between 1 and 95%, more preferably between 1 and 90%, even more preferably between 1 and 85%, and very preferably between 1 and 80% volume.

Advantageously according to the process of the invention, the boiling point of the polar solvent in the mixture of solvents according to the invention is above the boiling point of the apolar solvent.

The polar solvent used in the process according to the invention can be selected from the pure aromatic or naphthene-aromatic solvents, polar solvents comprising hetero-elements, or mixtures thereof. The aromatic solvent is advantageously selected from the monoaromatic hydrocarbons, preferably benzene, toluene or the xylenes alone or in a mixture; the diaromatics or polyaromatics; the naphthenic hydrocarbons-aromatic hydrocarbons such as tetralin or indane; the heteroatomic aromatic hydrocarbons (oxygen-containing, nitrogen-containing, sulphur-containing) or any other family of compounds having a more polar nature than the saturated hydrocarbons such as for example dimethylsulphoxide (DMSO), di-methyl formamide (DMF), tetrahydrofuran (THF). The polar solvent used in the process according to the invention can be a cut rich in aromatics. The cuts rich in aromatics according to the invention can be for example cuts originating from FCC (Fluid Catalytic Cracking) such as heavy gasoline or LCO (LCO (light cycle oil)) or originating from the petrochemical units of refineries. The cuts derived from coal, biomass or biomass/coal mixture optionally with a residual petroleum feedstock following thermochemical conversion with or without hydrogen, with or without catalyst may also be mentioned. Preferably, the polar solvent used is a monoaromatic hydrocarbon, pure or in a mixture with an aromatic hydrocarbon.

The apolar solvent used in the process according to the invention is preferably a solvent made up of saturated hydrocarbon(s) comprising a number of carbon atoms greater than or equal to 2, preferably comprised between 2 and 9. These solvents are used pure or in a mixture (for example: a mixture of alkanes and/or cycloalkanes or light petroleum cuts of the naphtha type).

Combined with the temperature and pressure conditions of the extraction according to the invention, the selection of the nature of the solvents, the selection of the combination of apolar/polar solvents in at least one of the stages of deasphalting makes it possible to access a minimum of two key points of adjustment in series which can be adjusted and which make it possible to access a range of selectivity previously inaccessible with conventional deasphalting. In the case of the present invention, the optimization of the two key points of adjustment makes it possible to separate the feedstock into three fractions: a fraction of asphalt referred to as final, enriched with impurities and compounds resistant to upcycling, a heavy deasphalted oil phase referred to as heavy DAO enriched with structures of the least polar resins and asphaltenes that are not refractory, and a light deasphalted oil phase referred to as light DAO depleted of resins and asphaltenes, and generally of impurities (metals, heteroatoms).

According to the process of the invention, the nature of the solvent and/or the proportion and/or the intrinsic polarity of the polar solvent in the mixture of solvents can be adjusted according to whether the asphalt is to be extracted during the first stage of deasphalting or during the second stage of deasphalting.

In a first embodiment, the process according to the invention is implemented in a configuration referred to as having decreasing polarity, i.e. the polarity of the mixture of solvents used during the first stage of deasphalting is higher than that of the solvent or mixture of solvents used during the second stage of deasphalting. This configuration makes it possible to extract, during the first stage of deasphalting, a fraction of asphalt phase referred to as final and a fraction of complete deasphalted oil referred to as complete DAO; the two fractions referred to as heavy deasphalted oil and light deasphalted oil being extracted from the complete deasphalted oil referred to as complete DAO during the second stage of deasphalting.

In a second embodiment, the process according to the invention is implemented in a configuration referred to as having increasing polarity, i.e. the polarity of the solvent or mixture of solvents used during the first stage of deasphalting is lower than that of the mixture of solvents used during the second stage of deasphalting. In such a configuration, during the first stage a fraction of deasphalted oil referred to as light and an effluent comprising an oil phase and an asphalt phase are extracted; said effluent being subjected to a second stage of deasphalting in order to extract a fraction of asphalt phase and a fraction of heavy deasphalted oil phase referred to as heavy DAO.

First Embodiment

According to this embodiment, the process according to the invention comprises at least:

-   -   a) a first stage of deasphalting comprising bringing the         feedstock into contact with a mixture of at least one polar         solvent and at least one apolar solvent, the proportions of said         polar solvent and said apolar solvent being adjusted so as to         obtain at least one fraction of asphalt phase and one fraction         of complete deasphalted oil phase referred to as complete DAO         and     -   b) a second stage of deasphalting comprising bringing at least a         part of the complete deasphalted oil phase referred to as         complete DAO originating from stage a) into contact with either         an apolar solvent or a mixture of at least one polar solvent and         at least one apolar solvent, the proportions of said polar         solvent and said apolar solvent in the mixture being adjusted so         as to obtain at least one fraction of light deasphalted oil and         one fraction of heavy deasphalted oil,         the stages of deasphalting a) and b) are implemented under the         subcritical conditions of the apolar solvent or mixture of         solvents used.

For a given feedstock, the higher the proportion and/or intrinsic polarity of the polar solvent in the mixture of solvents, the higher the yield of deasphalted oil, a part of the polar structures of the feedstock remaining solubilized and/or dispersed in the deasphalted oil DAO phase. Reducing the proportion of polar solvent in the mixture has the effect of increasing the quantity of asphaltenic phase collected.

The first stage of deasphalting thus makes it possible to extract selectively and in an optimal manner suited to each feedstock, a fraction of asphalt referred to as final, enriched with impurities and compounds resistant to upcycling, whilst leaving solubilized in the complete DAO oil matrix, all or part of the polar structures of the least polar heavy resins and asphaltenes which, for their part, are not resistant with respect to the downstream upcycling stages. Thus, depending on the proportion of apolar/polar solvent, the yield of deasphalted oil DAO can be significantly improved and the yield of asphalt therefore minimized. The asphalt yield can range from 0.1 to 50% and more particularly from 0.1 to 25%. This is a point of interest knowing that the upcycling of the asphalt (detrimental fraction) always constitutes a real limitation to systems including this type of process.

The complete deasphalted oil referred to as complete DAO originating from stage a) with, at least in part, the mixture of solvents according to the invention during the first stage of extraction, is preferably subjected to at least one stage of separation in which the complete deasphalted oil referred to as complete DAO is separated from the mixture of solvents according to the invention or at least one stage of separation in which the complete deasphalted oil referred to as complete DAO is separated from the apolar solvent only.

In a variant of the process, the complete deasphalted oil referred to as complete DAO originating from stage a) with, at least in part, the mixture of solvents according to the invention is subjected to two successive stages of separation making it possible to separate the solvents individually in each stage. Thus, for example, in a first stage of separation the apolar solvent is separated from the mixture of complete deasphalted oil referred to as complete DAO and polar solvent; and in a second stage of separation the polar solvent is separated from the complete deasphalted oil referred to as complete DAO.

The stages of separation are carried out under the supercritical or subcritical conditions.

At the end of the stage of separation, the complete deasphalted oil DAO separated from the mixture of solvents according to the invention is advantageously sent into at least one stripping column before being sent to the second stage of deasphalting.

The mixture of polar and apolar solvents or the individually separated solvents are advantageously recycled. In a variant of the process, only the apolar solvent is recycled into its respective makeup tank. When the recycled solvents are in a mixture, the apolar/polar proportion is verified on-line and readjusted as needed via makeup tanks individually containing the polar and apolar solvents. When the solvents are separated individually, said solvents are individually recycled into said respective makeup tanks.

The separated asphalt phase from the first stage of deasphalting is preferably in the liquid state and is generally diluted at least in part with a portion of the mixture of solvents according to the invention, the quantity of which can range up to 200%, preferably between 30 and 80% of the volume of asphalt drawn off. The asphalt extracted with, at least in part, the mixture of polar and apolar solvents at the end of the stage of extraction can be mixed with at least one fluxing agent so as to be drawn off more easily. The fluxing agent used can be any solvent or mixture of solvents that can solubilize or disperse the asphalt. The fluxing agent can be a polar solvent selected from the monoaromatic hydrocarbons, preferably benzene, toluene or xylene; the diaromatics or polyaromatics; the naphthene-hydrocarbons-aromatic hydrocarbons such as tetralin or indane; the heteroatomic aromatic hydrocarbons; the polar solvents with a molecular weight corresponding to boiling points comprised for example between 200° C. and 600° C. such as a LCO (light cycle oil from FCC), a HCO (heavy cycle oil from FCC), FCC slurry, HCGO (heavy coker gas-oil), or an aromatic extract or an extra-aromatic cut extracted from an oil chain, the VGO cuts originating from a conversion of residual fractions and/or of coal and/or of biomass. The ratio of volume of fluxing agent to the mass of the asphalt is determined so that the mixture can be easily drawn off.

The second stage of deasphalting can be implemented on at least a part, preferably the whole of the complete deasphalted oil referred to as complete DAO originating from the first stage of deasphalting in the presence of a mixture of at least one polar solvent and at least one apolar solvent under the subcritical conditions for the mixture of solvents used. The second stage of deasphalting can also be implemented on at least a part, preferably the whole of the complete deasphalted oil referred to as complete DAO originating from the first stage of deasphalting in the presence of an apolar solvent under the subcritical conditions for the solvent used. The polarity of said solvent or mixture of solvents is preferably lower than that of the mixture of solvents used in the first stage of deasphalting. This extraction is carried out so as to obtain a precipitated heavy deasphalted oil phase referred to as heavy DAO, predominantly comprising the family of the least polar resins and asphaltenes and a light deasphalted oil phase referred to as light DAO depleted of resins and asphaltenes, and generally of impurities (metals, heteroatoms). The light deasphalted oil phase referred to as light DAO predominantly comprises the family of the saturated hydrocarbons and the family of the aromatic hydrocarbons.

According to the invention, the separation selectivity and therefore the composition of the fractions of heavy deasphalted oil referred to as heavy DAO and light deasphalted oil referred to as light DAO can be modified by adjusting the polarity of the mixture of solvents by means of the nature and proportion of the apolar/polar solvents in the mixture or the nature of the apolar solvent.

Second Embodiment

In a second embodiment, the process according to the invention comprises at least:

-   -   a) a first stage of deasphalting comprising bringing the         feedstock into contact with either an apolar solvent, or a         mixture of at least one polar solvent and at least one apolar         solvent, the proportions of said polar solvent and said apolar         solvent in the mixture being adjusted so as to obtain at least         one fraction of light deasphalted oil phase and an effluent         comprising an oil phase and an asphalt phase; and     -   b) a second stage of deasphalting comprising bringing at least a         part of the effluent originating from stage a) into contact with         a mixture of at least one polar solvent and at least one apolar         solvent, the proportions of said polar solvent and said apolar         solvent being adjusted so as to obtain at least one fraction of         asphalt phase and a fraction of heavy deasphalted oil phase,         said stages of deasphalting being implemented under the         subcritical conditions of the apolar solvent or of the mixture         of solvents used.

In the present embodiment, the order of extraction of the categories of products is reversed: the polarity of the solvent or of the mixture of solvents used in the first stage of deasphalting is lower than that of the mixture of solvents used in the second stage of deasphalting.

The first stage of deasphalting thus makes it possible to selectively extract from the feedstock a fraction of light deasphalted oil referred to as light DAO and an effluent comprising an oil phase and an asphalt phase. The first stage of deasphalting can be implemented both on an apolar solvent and on a mixture of solvents according to the invention. The nature, the proportion and/or the polarity of the polar solvent in the mixture of solvents is adapted, under the subcritical conditions of the solvent or of the mixture of solvents used, so as to extract a fraction of light deasphalted oil predominantly comprising the family of the saturated hydrocarbons and the family of the aromatic hydrocarbons.

The effluent comprising a heavy deasphalted oil phase referred to as heavy DAO and an extracted asphalt phase from the first stage of deasphalting can contain, at least in part, the apolar solvent or the mixture of solvents according to the invention. Advantageously according to the invention, said effluent is subjected to at least one stage of separation in which it is separated from the apolar solvent or from the mixture of solvents according to the invention or at least one stage of separation in which said effluent is separated only from the apolar solvent contained in the mixture of solvents.

In a variant of the process according to the invention, said effluent can be subjected to at least two successive stages of separation making it possible to separate the solvents individually in each stage of separation (as described in the first embodiment of the invention).

The stages of separation are carried out under supercritical or subcritical conditions.

At the end of the stage of separation, the effluent comprising the heavy deasphalted oil phase referred to as heavy DAO and the asphalt phase separated from the solvent or from the mixture of solvents according to the invention can be sent into at least one stripping column before being sent to the second stage of deasphalting.

The mixture of polar and apolar solvents or the individually separated solvents are advantageously recycled. In a variant of the process, only the apolar solvent is recycled into its respective makeup tank. When the recycled solvents are in a mixture, the proportion of the apolar and polar solvents is verified on-line and readjusted as needed via makeup tanks containing said polar and apolar solvents individually. When the solvents are separated individually, said solvents are individually recycled into said respective makeup tanks.

The second stage of deasphalting is implemented on at least a part, preferably the whole of the effluent comprising a heavy deasphalted oil phase referred to as heavy DAO and an asphalt phase originating from the first stage of deasphalting in the presence of a mixture of at least one polar solvent and at least one apolar solvent under the subcritical conditions for the mixture of solvents used. The polarity of said mixture of solvents is preferably higher than that of the solvent or of the mixture of solvents used in the first stage of deasphalting. This extraction is carried out so as to selectively extract from the effluent, a fraction of asphalt referred to as final, enriched with impurities and compounds resistant to upcycling, whilst leaving solubilized in the heavy deasphalted oil matrix referred to as heavy DAO, all or part of the polar structures of the least polar resins and asphaltenes remaining generally contained in the fraction of asphalt in the case of conventional deasphalting.

The process according to the invention has the advantage of allowing a significant improvement in the total yield of light and heavy deasphalted oils referred to as light DAO and heavy DAO over an entire range previously unexplored by conventional deasphalting. For a given feedstock for which the total yield of light and heavy deasphalted oils obtained levels off at 75% (extraction with normal heptane in conventional deasphalting), the deasphalting implemented in the invention makes it possible, under specific conditions, to cover the range of 75-99.9% of total yield of light and heavy deasphalted oils referred to as light DAO and heavy DAO, by adjustment of the proportion of polar solvent and apolar solvent.

The process according to the invention, due to its separation selectivity and its flexibility, makes it possible to obtain a fraction of asphalt with a yield of asphalt much lower than that which can be obtained by a conventional deasphalting process in the case of a given feedstock. Said yield of asphalt is advantageously comprised between 1 and 50%, preferably between 1 and 25%, more preferably between 1 and 20%.

The present invention has the advantage: i) of an improvement in the properties of the feedstocks treated allowing easier and more efficient upcycling whilst ii) limiting the yield of asphalt in a controlled manner.

Thanks to two key points of adjustment, the process according to the invention has the advantage of improved flexibility with respect to:

-   -   the nature of the feedstock: the invention is suited to the         treatment of a wider range of feedstock,     -   the upcycling of the products: depending on the upcycling route         of the products sought, the invention makes it possible to         orient the selectivity of the separation towards obtaining         fractions of heavy deasphalted oil referred to as heavy DAO and         light deasphalted oil referred to as light DAO optimized in         terms of yield and/or chemical composition.

The fraction of light deasphalted oil referred to as light DAO can for example be upcycled as feedstock for hydrocracking, FCC (in order to increase the upcycling of gasoline for example) or for any other refining treatment process. The fraction of heavy deasphalted oil referred to as heavy DAO can for example be upcycled as feedstock for hydrotreatment, hydroconversion or any other refining treatment process, but also recycled in certain refining processes.

DESCRIPTION OF THE FIGURES

According to an embodiment of the invention described in FIG. 1, the feedstock (1) heated beforehand using furnaces and/or exchangers (not shown) is introduced into an extractor (13) such as an extraction column, preferably a mixer-settler. The mixture of polar solvent (3) and apolar solvent (2) is produced upstream in a mixer (10) fed by two makeup tanks each filled separately with polar solvent (tank 4) and apolar solvent (tank 5). The mixture of solvents is for example introduced into the extractor (13) at two different levels. At least a part of the mixture of solvents is sent via the conduit 11 in a mixture with the introduced feedstock into the extractor (13) via the conduit 1. At least one other part of the mixture of solvents is sent via the conduit (12) directly into the extractor (13) in which the extraction is carried out under conditions according to the invention defined above.

According to FIG. 1, the asphalt (16) also containing, at least in part, the mixture of solvents according to the invention, is drawn off from the extractor (13) in the form of a liquid mixture or in the form of a dispersed solid using a fluxing agent sent via the conduit 14. The mixture of asphalt, solvent according to the invention and fluxing agent can then be sent to an additional stage of separation that is not shown. The separated solvents or part of the solvents or fluxing agent can be reused in the process of the invention.

At the end of the first stage of extraction, the complete deasphalted oil referred to as extracted complete DAO, in a mixture with, at least in part, the mixture of solvents according to the invention is sent via the conduit 15 to the separator (17) in which the complete deasphalted oil is separated from the mixture of solvents or only from the apolar solvent contained in the mixture of solvents (22). The process can comprise a second separator (see FIG. 2) in the case where the solvents are separated individually. The mixture of solvents or the solvents taken individually are advantageously separated in the separator under supercritical or subcritical conditions. The complete deasphalted oil is then preferably sent into a stripping column (19) via the conduit (18), before being recovered via the conduit (20). The solvent originating from the stripping column is sent to the line (23) via the conduit (21).

The solvent originating from the separator (17) and the stripping column (21) is advantageously recycled internally in the process via the line (23) to the extractor (13). The composition of the mixture of polar and apolar solvents is preferably verified on-line by a density meter or a refractometer (24). The proportions of polar solvent and apolar solvent are, as needed, readjusted with a makeup of polar solvent and apolar solvent respectively conveyed from the makeup tanks (4) and (5) via the conduits (6) and (7). The mixture readjusted in this way is advantageously homogenized in a static-type mixer (25) before being sent into the mixer (10). When the solvents are separated individually, each solvent is recycled into its original tank.

The complete deasphalted oil recovered via the conduit (20) is then sent to a second extractor (37) utilized under conditions according to the invention and making it possible to separate a fraction of light deasphalted oil referred to as light DAO (38) and a fraction of heavy deasphalted oil referred to as heavy DAO (39). The mixture of polar solvent (27) and apolar solvent (26) is produced upstream in a mixer (34) fed by two makeup tanks each filled separately with polar solvent (tank 28) and apolar solvent (tank 29). The polar and apolar solvents can be different from those used in the first extractor. In the case where the polar and apolar solvents used in the two extractors are identical, the mixture of solvents used in the second extractor can be fed by the two makeup tanks (4) and (5). Otherwise, the mixture of solvents used in the second extractor is fed by the two makeup tanks (28) and (29). In another case in point, only the apolar solvent (26) can be utilized.

The fraction of light deasphalted oil referred to as light DAO (38) extracted in a mixture with, at least in part, the apolar solvent or the mixture of solvents according to the invention is sent to a separator (40) in which the light deasphalted oil referred to as light DAO (41) is separated, in part or not, from the solvent according to the invention (45). The process can comprise a second separator in the case where the solvents are separated individually as described above in the case of the mixture of solvents. The mixture of solvents or the solvents taken individually are advantageously separated in the separator under supercritical or subcritical conditions. The light deasphalted oil referred to as light DAO (41) is then preferably sent into a stripping column (42), before being recovered via the conduit (43). The solvent originating from the stripping column is sent to the line (46) via the conduit (44).

The fraction of extracted heavy deasphalted oil referred to as heavy DAO (39) in a mixture with, at least in part, the apolar solvent or the mixture of solvents according to the invention is sent to a separator (49) in which the heavy deasphalted oil referred to as heavy DAO (50) is separated from the apolar solvent or from the solvent according to the invention or only from the apolar solvent contained in the mixture of solvents (53). The mixture of solvents or the solvents taken individually are advantageously separated in the separator under supercritical or subcritical conditions. The heavy deasphalted oil referred to as heavy DAO (50) is then preferably sent into a stripping column (51), before being recovered via the conduit (52). The solvent originating from the stripping column is sent to the line (46) via the conduit (54).

The solvents originating from the separators (40, 49), of the stripping columns (42, 51) are advantageously recycled internally in the process via the line (46) to the extractor (37). In the case of a mixture of solvents, the composition of the mixture of polar and apolar solvents is preferably verified on-line by a density meter or a refractometer (47). The proportions of polar solvent and apolar solvent are, as needed, readjusted with a makeup of polar solvent and apolar solvent conveyed from the makeup tanks (28) and (29) or from the makeup tanks (4) and (5) according to whether the solvents used in the second extractor are identical to or different from those used in the first extractor. The mixture readjusted in this way is advantageously homogenized in a static-type mixer (48) before being sent to the mixer (34). When the solvents are separated individually, each solvent is recycled into its original tank.

FIG. 2 shows a diagram of the process according to the invention incorporating two separators (17) and (20) making it possible to separate the solvents individually and recycle them individually into their respective tanks. Thus according to FIG. 2, the feedstock (1) heated beforehand using furnaces and/or exchangers (not shown) is introduced into an extractor (13) such as an extraction column, preferably a mixer-settler. The mixture of polar solvent (3) and apolar solvent (2) is produced upstream in a mixer (10) fed by two makeup tanks, each filled separately with polar solvent (tank 4) and apolar solvent (tank 5). The mixture of solvents is for example introduced into the extractor (13) at two different levels. At least a part of the mixture of solvents is sent via the conduit (11) in a mixture with the introduced feedstock into the extractor (13) via the conduit (1). At least one other part of the mixture of solvents is sent via the conduit 12 directly into the extractor (13) in which the extraction is carried out under conditions according to the invention defined above.

The asphalt (16) also containing, at least in part, the mixture of solvents according to the invention is drawn off from the extractor (13) in the form of a liquid mixture or in the form of a dispersed solid using a fluxing agent sent via the conduit (14). The asphalt (16) can be subjected to the same treatment as that described for FIG. 1.

At the end of the first stage of extraction, the extracted complete deasphalted oil referred to as complete DAO in a mixture with, at least in part, the mixture of solvents according to the invention is sent via the conduit (15) to the separator (17) in which the complete deasphalted oil referred to as complete DAO is preferably separated from the apolar solvent (19). The apolar solvent is advantageously recycled into the tank (5). The complete deasphalted oil referred to as complete DAO, in a mixture with the polar solvent, is then sent via the conduit (18) to the second separator (20) in which the complete deasphalted oil referred to as complete DAO is separated from the polar solvent (21) sent to the line (26). The solvents are advantageously separated in the separators under supercritical or subcritical conditions. The complete deasphalted oil referred to as complete DAO is then preferably sent into a stripping column (23) via the conduit (22), before being recovered via the conduit (24). The solvent originating from the stripping column is sent to the line (26) via the conduit (25). The polar solvent originating from the separator (20) and the stripping column (23) is recycled into the tank (4) via the line (26).

The complete deasphalted oil referred to as complete DAO recovered via the conduit (24) is then sent to a second extractor (38). The separated fractions of deasphalted oil are subjected to the same treatment as that described above in FIG. 1.

EXAMPLES

The feedstock selected for the examples is a vacuum residue originating from Athabasca in northern Canada. Its chemical characteristics are given in Table 1.

Example 1 Not According to the Invention

Example 1 corresponds to the implementation of conventional two-stage deasphalting as described in the patent US 2008149534. The selected feedstock has been subjected to a first deasphalting with the paraffinic solvent normal heptane, then the collected deasphalted oil C7 DAO has been subjected to a second deasphalting with normal propane in order to obtain the heavy DAO and light DAO fractions. The properties as well as the extraction yields of each of the fractions are summarized in Table 1.

The yield of C7 DAO is 75% for a C7 asphaltenes content (measured according to the standard NFT60-115) of 14%. This shows that a part of the resins has also been extracted with the C7 asphaltenes in order to constitute the asphalt.

TABLE 1 Properties of the feedstock as well as yields and properties of the fractions originating from the conventional two-stage deasphalting carried out with the solvents nC7 for the first stage then nC3 for the second stage. Initial Athabasca 1st stage 2nd stage Residue Asphalt DAO heavy DAO light DAO 480° C.+ nC7 nC7 nC3 nC3 Extraction (% of 100 25 75 41 34 yield feedstock) Analyses d4, 15 — 1.044 1.11 1.021 1.059 0.974 Sulphur % m/m 5.72 7.90 5.00 6.22 3.50 Nitrogen ppm 6200 7944 5625 8927 1581 Ni ppm 115 306 52 93 2 V ppm 317 823 150 268 5 CCR % m/m 20.5 45 12.4 20.5 2.5

In this example, the yields as well as the qualities of the various DAOs are fixed by the nature of the paraffinic solvent used in each of the two stages.

Example 2 According to the Invention

The feedstock selected is subjected to the selective two-stage deasphalting according to the invention. The first stage of extraction is carried out with the combination of solvent nC3 (propane)/toluene (36/65; v/v) at a temperature of 130° C., the solvent/feedstock ratio is 5/1 (v/m). This first stage has made it possible to selectively extract 50% of the C7 asphaltenes from the fraction of asphalt, whilst minimizing the asphalt yield thereof (10% m/m) (see Table 2). The first stage makes it possible to upcycle 90% of the residue (deasphalted oil DAO yield of 90%). The most polar structures in the feedstock are concentrated in the fraction of asphalt.

The fraction of deasphalted oil DAO originating from the first stage of deasphalting is then separated from the solvent according to the invention before being subjected to the second stage of extraction. Cases No. 1 and No. 2 illustrate the flexibility of the process according to the quality or the envisaged yield of the separated fractions depending on the specifications required for the units situated downstream.

Case No. 1: Obtaining a Good-Quality Fraction of Light Deasphalted Oil

The second stage of extraction is carried out on the fraction of deasphalted oil DAO originating from the first stage of deasphalting with the same solvents as in the first stage of Example 2, propane (nC3) and toluene. In this case No. 1, the proportions of propane (nC3) and toluene are adjusted in order to meet the objective of obtaining a fraction of good-quality light deasphalted oil referred to as light DAO. The operation is carried out with a mixture of solvents nC3/toluene (99.5/0.5; v/v), a temperature of 120° C. and a solvent/DAO ratio of 5/1 (v/m). A fraction of heavy deasphalted oil referred to as heavy DAO and a fraction of light deasphalted oil referred to as light DAO are obtained, with respective yields of 54% and 36% (yields calculated with respect to the initial feedstock residue). All of the results are summarized in Table 2.

TABLE 2 Yield and properties of the fractions originating from the selective two-stage deasphalting carried out in the case of obtaining a light DAO fraction of good quality. Initial 1st stage 2nd stage Athabasca Asphalt DAO heavy DAO light DAO residue nC3/toluene nC3/toluene nC3/toluene nC3/toluene 480° C.+ (35/65; v/v) (35/65; v/v) (99.5/0.5; v/v) (99.5/0.5; v/v) Extraction (% of 100 10 90 54 36 yield feedstock) Analyses d4, 15 — 1.044 na 1.029 1.064 0.976 Sulphur % m/m 5.72 9.32 5.32 6.49 3.56 Nitrogen ppm 6200 8900 5900 8431 2103 Ni ppm 115 511 71 116 3 V ppm 317 1460 190 313 6 CCR % m/m 20.5 >50 16.3 25.4 2.6 *na: not analyzable.

It is noted that the qualities of the fraction of light deasphalted oil obtained in Example 1, are very close to those obtained in the light deasphalted oil according to the invention, with the yield of light deasphalted oil according to the invention being identical.

The fraction of heavy deasphalted oil referred to as heavy DAO obtained according to the invention is enriched with the least polar resins and asphaltenes. This fraction has a marked aromatic nature and a higher concentration of impurities (metals, heteroatoms) than the fraction of light deasphalted oil referred to as light DAO. If the properties of this fraction are compared to those of the heavy deasphalted oil of Example 1, it is noted that they are richer in heavy structures but can be upcycled, unlike Example 1 where these structures remain non-upcycled as they are contained in the fraction of asphalt. The yield of heavy deasphalted oil referred to as heavy DAO produced that can be upcycled is clearly improved (54% as against 41% in the case of the conventional SDA of Example 1).

Case No. 2: Obtaining the Fraction of Light Deasphalted Oil Referred to as Light DAO with a Better Yield

The second stage of extraction is carried out on the DAO originating from the first stage of deasphalting with the same solvents as in the first stage of Example 2, propane (nC3) and toluene. In this case No. 2, the proportions of propane (nC3) and toluene are adjusted in order to meet the objective of obtaining a light deasphalted oil referred to as light DAO with a high yield. The extraction conditions of the first stage of the process remain unchanged. The operation is carried out with a mixture of solvents nC3/toluene (72/28 (v/v)). The temperature is 125° C. and the solvent/DAO ratio is 5/1 (v/m).

The results shown in Table 3 show that the fraction of light deasphalted oil referred to as light DAO is obtained with a yield of 60% instead of 36% in case No. 1. On the other hand, this deasphalted oil now contains a part of the least polar resins. Consequently, the yield of the heavy deasphalted oil referred to as heavy DAO is reduced from 54 to 30% (compared with case No. 1) and it concentrates a majority of the least polar asphaltenes and the most polar resins. This heavy deasphalted oil can be recycled and is sought depending on the objective of the system in which the invention is incorporated.

The advantage of using a combination of apolar/polar solvent is being able to adjust and optimize as desired and without limitation the yield (unlike conventional deasphalting), the yield/quality relationship of the extracted fractions originating from the stages of deasphalting for a given feedstock and for an objective of a given system. There is no longer any restriction imposed by the nature of the solvents as in the case of conventional deasphalting, which is what gives the process all its flexibility.

TABLE 3 Yield and properties of the fractions originating from the selective two-stage deasphalting carried out in the case of obtaining a fraction of light deasphalted oil referred to as light DAO, with a better yield. Initial 1st stage 2nd stage Athabasca Asphalt DAO heavy DAO light DAO residue nC3/toluene nC3/toluene nC3/toluene nC3/toluene 480° C.+ (35/65; v/v) (35/65; v/v) (72/28; v/v) (72/28; v/v) Extraction (% of 100 10 90 30 60 yield feedstock) Analyses d4, 15 — 1.044 na 1.029 1.105 0.991 Sulphur % m/m 5.72 9.32 5.32 8.00 3.98 Nitrogen ppm 6200 8900 5900 7496 5102 Ni ppm 115 511 71 151 31 V ppm 317 1460 190 324 123 CCR % m/m 20.5 >50 16.3 33.9 7.5 *na: not analyzable. 

1. Process for the deasphalting of a heavy feedstock by liquid/liquid extraction, said process comprising at least two stages of deasphalting in series carried out on the feedstock to be treated, making it possible to separate at least one fraction of asphalt, at least one fraction of heavy deasphalted oil, referred to as heavy DAO and at least one fraction of light deasphalted oil, referred to as light DAO, at least one of said stages of deasphalting being carried out by means of a mixture of at least one polar solvent and at least one apolar solvent, the proportions of said polar solvent and said apolar solvent in the mixture of solvents being adjusted according to the properties of the feedstock treated and according to the desired yield of asphalt and/or the quality of the deasphalted oil, said stages of deasphalting being implemented under the subcritical conditions of the mixture of solvents used.
 2. Process according to claim 1 comprising at least: a) a first stage of deasphalting comprising bringing the feedstock into contact with a mixture of at least one polar solvent and at least one apolar solvent, the proportions of said polar solvent and said apolar solvent being adjusted so as to obtain at least one fraction of asphalt phase and one fraction of complete deasphalted oil phase referred to as complete DAO; and b) a second stage of deasphalting comprising bringing at least a part of the deasphalted oil phase originating from stage a) into contact with either an apolar solvent, or a mixture of at least one polar solvent and at least one apolar solvent, the proportions of said polar solvent and said apolar solvent in the mixture being adjusted so as to obtain at least one fraction of light deasphalted oil and one fraction of heavy deasphalted oil, said stages of deasphalting being implemented under the subcritical conditions of the apolar solvent or of the mixture of solvents used.
 3. Process according to claim 2, in which the deasphalted oil phase originating from stage a) is previously subjected to at least one stage of separation in which the deasphalted oil is separated from the mixture of solvents or at least one stage of separation in which the complete deasphalted oil referred to as complete DAO is separated only from the apolar solvent.
 4. Process according to claim 2, in which the deasphalted oil phase originating from stage a) is previously subjected to at least two successive stages of separation in which the polar and apolar solvents are separated individually.
 5. Process according to claim 3 in which the deasphalted oil separated from the solvents is sent into at least one stripping column before being sent into the second stage of deasphalting.
 6. Process according to claim 1 comprising at least: a) a first stage of deasphalting comprising bringing the feedstock into contact with either an apolar solvent, or a mixture of at least one polar solvent and at least one apolar solvent, the proportions of said polar solvent and said apolar solvent in the mixture being adjusted so as to obtain at least one fraction of light deasphalted oil phase and an effluent comprising an oil phase and an asphalt phase; and b) a second stage of deasphalting comprising bringing at least a part of the effluent originating from stage a) into contact with a mixture of at least one polar solvent and at least one apolar solvent, the proportions of said polar solvent and said apolar solvent being adjusted so as to obtain at least one fraction of asphalt phase and one fraction of heavy deasphalted oil phase, said stages of deasphalting being implemented under the subcritical conditions of the apolar solvent or of the mixture of solvents used.
 7. Process according to claim 6, in which the effluent originating from stage a) is previously subjected to at least one stage of separation in which the effluent is separated from the apolar solvent or from the mixture of solvents or at least one stage of separation in which said effluent is separated only from the apolar solvent contained in the mixture of solvents.
 8. Process according to claim 6, in which the effluent originating from stage a) is previously subjected to at least two stages of separation in which the polar and apolar solvents are individually separated.
 9. Process according to claim 7 in which the effluent separated from the solvents is sent into at least one stripping column before being sent into the second stage of deasphalting.
 10. Process according to claim 1 in which the proportion of polar solvent in the mixture of polar solvent and apolar solvent in at least one of the stages of deasphalting is comprised between 0.1 and 99.9% volume.
 11. Process according to claim 1 in which the polar solvent used is selected from the pure aromatic or naphthene-aromatic solvents, the polar solvents comprising hetero-elements, or a mixture thereof or cuts rich in aromatics such as cuts originating from FCC (Fluid Catalytic Cracking) or originating from the petrochemical units of refineries, cuts derived from coal, biomass or biomass/coal mixture.
 12. Process according to claim 1 in which the apolar solvent used comprises a solvent made up of saturated hydrocarbon(s) comprising a carbon number greater than or equal to 2, preferably comprised between 2 and
 9. 13. Process according to claim 1 in which the feedstock is selected from the feedstocks of petroleum origin of crude oil type, atmospheric residue, vacuum residue type originating from so-called conventional crude, heavy crude or extra heavy crude, a residual fraction originating from any pre-treatment or conversion process such as hydrocracking, hydrotreatment, thermal cracking, hydroconversion of one of these crudes or of one of these atmospheric residues or one of these vacuum residues, a residual fraction originating from the direct liquefaction of ligno-cellulosic biomass alone or in a mixture with coal and/or a fraction of residual petroleum.
 14. Process according to claim 3 in which, when the recycled solvents are in a mixture, the apolar/polar proportion is verified on-line and readjusted as needed via makeup tanks individually containing the polar and apolar solvents.
 15. Process according to claim 3 in which, when the solvents are separated individually, said solvents are individually recycled into said respective makeup tanks. 